Formation of Jupiter-Mass Binary Objects through photoerosion of fragmenting cores

Abstract: The recent discovery of tens of Jupiter-mass binary objects (JuMBOs) in the Orion Nebula Cluster with the James Webb Space Telescope has intensified the debate on the origin of free-floating planetary mass objects within star-forming regions. The JuMBOs have masses below the opacity limit for fragmentation, but have very wide separations (10s - 100s au), suggesting that they did not form in a similar manner to other substellar mass binaries. Here, we propose that the theory of photoerosion of prestellar cores by Lyman continuum radiation from massive stars could explain the JuMBOs in the ONC. We find that for a range of gas densities the final substellar mass is comfortably within the JuMBO mass range, and that the separations of the JuMBOs are consistent with those of more massive (G- and A-type) binaries, that would have formed from the fragmentation of the cores had they not been photoeroded. The photoerosion mechanism is most effective within the HII region(s) driven by the massive star(s). The majority of the observed JuMBOs lie outside of these regions in the ONC, but may have formed within them and then subsequently migrated due to dynamical evolution.

• The paper proposes photoerosion of fragmenting protostellar cores as a viable mechanism to explain the mass distribution and wide separations observed in Jupiter-Mass Binary Objects (JuMBOs).
• The study demonstrates that the mass range and wide separation characteristics of JuMBOs are consistent with formation via photoerosion acting on cores that would typically form higher-mass stellar binaries.
• This research suggests that JuMBOs may initially form within ionized HII regions through photoerosion before potentially migrating outwards due to dynamical interactions in dense star clusters like the Orion Nebula Cluster.

Formation of Jupiter-Mass Binary Objects through Photoerosion of Fragmenting Cores

The study by Diamond and Parker addresses the intriguing formation of Jupiter-Mass Binary Objects (JuMBOs) in the Orion Nebula Cluster (ONC), a discovery facilitated by the James Webb Space Telescope. This paper revisits the longstanding astrophysical enigma of free-floating planetary mass objects, particularly focusing on how these objects can exist with wide separations ranging from tens to hundreds of astronomical units (au), contrary to expectations from conventional star formation theories which predict much closer separations for substellar binaries.

Summary of Findings

The authors propose that these JuMBOs could be products of the photoerosion process in star-forming regions, a theory developed to explain low-mass object formation in environments with intense radiation from massive stars. The presence of massive stars in regions like the ONC can induce photoerosion, altering the mass distribution within protostellar cores and potentially leading to the formation of binary systems like those observed.

Key Findings Include:

1. Mass Distribution Compatibility: The mass range of JuMBOs aligns well with objects formed via photoerosion. The analysis reveals that the final mass distributions post-photoerosion comfortably fit within the observed JuMBO masses, particularly under varying hydrogen density conditions.
2. Separation Distribution Explanation: The JuMBOs’ wide separation distribution is more consistent with that of higher-mass binaries (like G- and A-type stars) rather than traditional brown dwarf binaries, suggesting a different formation process. Photoerosion acting on fragmenting cores that would otherwise form such stellar binaries accounts for this separation range.
3. Dynamical Migration Hypothesis: Considering the majority of the observed JuMBOs lie outside the current HII regions, the authors suggest that these objects may have initially formed within such ionized regions but subsequently migrated due to dynamical interactions within the densely packed ONC.

Analytical Model and Methodology

The study leverages the Whitworth et al. (2004) framework of core photoerosion, applying it to the ONC’s star-forming conditions. Simulations were carried out considering the effects of Lyman continuum radiation on fragmenting cores. The theoretical modeling considers a range of hydrogen nuclei densities, reflecting the complex environmental conditions within the ONC and the influence of massive stars such as those in the Trapezium system.

Implications and Future Directions

Astrophysical Impact: The findings have significant implications for understanding the formation and evolution of low-mass celestial objects in star clusters. By linking the physical processes of photoerosion to the distribution characteristics of JuMBOs, the paper provides a coherent explanation that challenges traditional paradigms of isolated star and planet formation.

Theoretical Extensions: Extending this model to other star-forming regions with similar conditions could verify the ubiquity and robustness of photoerosion as a mechanism. Moreover, further detailed simulations incorporating more complex interactions, such as magnetohydrodynamic effects and radiative transfer processes, could provide deeper insights.

Observational Prospects: Future observations, particularly those that can delineate the motion and distribution of JuMBOs and similar objects in other regions, will be pivotal in testing these hypotheses. JWST and forthcoming observational platforms will be crucial in identifying and characterizing more such systems, thereby refining our understanding of substellar object formation.

In conclusion, Diamond and Parker's research contributes significantly to the discourse on planetary formation under high-radiation astrophysical contexts, providing a plausible mechanism for the nature and distribution of JuMBOs in dense star-forming environments.